Determination of temperature from experimental data has become important in searches for critical phenomena in heavy-ion collisions. Widely used methods are ratios of isotopes (which rely on chemical and thermal equilibrium), population ratios of excited states, etc. Using the lattice gas model we propose a new observable: ${\mathit{n}}_{\mathrm{ch}}$/Z where ${\mathit{n}}_{\mathrm{ch}}$ is the charge multiplicity and Z is the charge of the fragmenting system. We show that the reduced multiplicity is a good measure of the average temperature of the fragmenting system. © 1996 The American Physical Society.

• Received 21 August 1996

DOI:https://doi.org/10.1103/PhysRevC.54.R2820